功能描述：
function [patterns, targets] = AGHC(train_patterns, train_targets, params, plot_on)

%Reduce the number of data points using the agglomerative hierarchical clustering algorithm
%Inputs:
% train_patterns - Input patterns
% train_targets - Input targets
% params - Parameters: [Number of output data points, distance type]
%   Distance can be min, max, avg, or mean
%   plot_on         - Plot stages of the algorithm
%
%Outputs
% patterns - New patterns
% targets - New targets

if (nargin < 4),
    plot_on = 0;
end

[c, method] = process_params(params);
[D,c_hat] = size(train_patterns);
label       = 1:c_hat;
n           = ones(1,c_hat);

%Compute distances
N           = size(train_patterns,2);
temp        = repmat(train_patterns,[1 1 N]);
dist        = sqrt(squeeze(sum((temp - permute(temp, [1 3 2])).^2)));

while (c_hat > c),
    Uc       = unique(label);
    Nc       = length(Uc);
    new_dist = zeros(Nc);

    switch method
    case 'min'
        %Find minimum distance between vectors from different clusters
        
        %For each two clusters, find the shortest distance between vectors
        for i = 1:Nc,
            i_in = find(label == Uc(i));
            for j = 1:Nc,
                j_in = find(label == Uc(j));
                new_dist(i,j) = min(min(dist(i_in,j_in)));
            end
        end
        new_dist    = new_dist + eye(Nc)*1e33;
        [i,j]   = find(new_dist == min(min(new_dist)));
        i = Uc(i(1)); j = Uc(j(1));
    case 'max'
        %Find maximum distance between vectors from different clusters
        
        %For each two clusters, find the longest distance between vectors
        for i = 1:Nc,
            i_in = find(label == Uc(i));
            for j = 1:Nc,
                j_in = find(label == Uc(j));
                new_dist(i,j) = max(max(dist(i_in,j_in)));
            end
        end
        new_dist = new_dist .* (ones(Nc)-eye(Nc));
        [i,j]   = find(new_dist == max(max(new_dist)));
        i = Uc(i(1)); j = Uc(j(1));
        
    case 'avg'
        %Find average distance between vectors from different clusters
        
        %For each two clusters, find the average distance between vectors in one cluster to each vector in the other cluster
        for i = 1:Nc,
            i_in = find(label == Uc(i));
            for j = 1:Nc,
                j_in = find(label == Uc(j));
                new_dist(i,j) = mean(mean(dist(i_in,j_in)))/(length(j_in)*length(i_in));
            end
        end
        new_dist = new_dist .* (ones(Nc)-eye(Nc));
        [i,j]   = find(new_dist == max(max(new_dist)));
        i = Uc(i(1)); j = Uc(j(1));
        
    case 'mean'
        %Find mean distance between cluster centers 
        
        %For each two clusters, find the average distance between vectors in one cluster to each vector in the other cluster
        for i = 1:Nc,
            i_in = find(label == Uc(i));
            for j = 1:Nc,
                j_in = find(label == Uc(j));
                new_dist(i,j) = sum((mean(train_patterns(:,i_in)')'-mean(train_patterns(:,j_in)')').^2);
            end
        end
        new_dist    = new_dist + eye(Nc)*1e33;
        [i,j]   = find(new_dist == min(min(new_dist)));
        i = Uc(i(1)); j = Uc(j(1));
    otherwise
        error('Distance method unknown')
    end
      
    %Merge cluster i with cluster j
    label(find(label == j)) = i;
    
    c_hat = c_hat - 1;
    
    %Computer cluster centers
    Uc       = unique(label);
    Nc       = length(Uc);
    patterns = zeros(D,Nc);
    for i = 1:Nc,
        in            = find(label == Uc(i));
        if (length(in) == 1)
            patterns(:,i) = train_patterns(:,in);
        else
            patterns(:,i) = mean(train_patterns(:,in)')';
        end
    end
    
    %Plot the centers during the process 
    plot_process(patterns, plot_on)
    
end
 
%Label the data
targets = zeros(1,c);
Uc      = unique(label);
Ut      = unique(train_targets);
targets = zeros(1,c);
for i = 1:c,
    indices    = find(label == Uc(i));
    N          = hist(train_targets(:,indices), Ut);
    [m, max_l] = max(N);
    targets(i) = Ut(max_l);
    if (length(indices) == 1)
        patterns(:,i) = train_patterns(:,indices);
    else
        patterns(:,i) = mean(train_patterns(:,indices)')';
    end
end

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